Why doesn't Gedit recognize my Super_L modifier key?

--- Introduction ---

I'm running Kubuntu 10.04. Gedit is my primary text editor. There is a Snippets plugin for Gedit that allows you to assign custom keyboard shortcuts for pasting snippets into your code. For many of these shortcuts I use the Super key, to avoid conflicts with other shortcuts.

When I'm assigning shortcuts in the snippets editor, everything works as expected. Pressing the Super key and the s key, for instance, yields the shortcut Super+s. But when I'm in the editor itself, pressing that same key combo yields only the letter 's'.

I've been trying to solve this problem for days now (details below), and I would give up if only this hadn't worked flawlessly when I was running 9.10. So I know it can be done!

--- Diagnostic Efforts ---

I don't know all that much about key mappings and keyboard layouts, but I've spent several days reading (and trying) pretty much everything I could find. Here's what I've done to try to understand the problem:

1) I've run xev and recorded the output when pressing the left Super key:

KeyPress event, serial 34, synthetic NO, window 0x3800001,
    root 0x123, subw 0x0, time 20661147, (170,-2), root:(913,610),
    state 0x10, keycode 133 (keysym 0xffeb, Super_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

Seems to be recognized correctly as the Super key. And as I said above, when assigning the shortcuts in the Gedit snippets editor, it is correctly recognized.

2) I've run xmodmap, and recorded the output:

shift Shift_L (0x32), Shift_R (0x3e)
lock Caps_Lock (0x42)
control Control_L (0x25), Control_R (0x69)
mod1 Alt_L (0x40), Meta_L (0xcd)
mod2 Num_Lock (0x4d)
mod3
mod4 Super_L (0x85), Super_R (0x86), Super_L (0xce), Hyper_L (0xcf)
mod5 ISO_Level3_Shift (0x5c), Mode_switch (0xcb)

3) I've tried to use the Super key in KDE to assign shortcuts. It's shown as Meta rather than Super, but I can successfully assign and use KDE shortcuts using the button.

4) I've tested other GTK apps as well—none of them seem to recognize it as a modifier key. Holding the Super key and pressing any other letter simply produces the letter.

--- Efforts to Solve the Problem ---

1) First thing I did, of course, was to try various keyboard layout options in the KDE system settings, especially the Alt/Win Key Behavior settings. I have tried every single option, logging out and restarting X after each one, to no avail.

2) I've also tried all kinds of xmodmap commands, removing and reassigning the keys and so forth, all to no avail.

3) I even installed the whole Gnome control center and tried editing the keyboard settings there thinking maybe I was just missing some gnome configuration file, to no avail.

So is there something I'm missing here? Any place I haven't looked? Any help at all would be greatly appreciated.